The rough coat (rc) phenotype, which arose spontaneously as a recessive trait in C57BL/6J mice, is characterized by an unkempt-looking coat, cyclic and progressive hair loss, and ulcerative skin lesions. Follicular atrophy and persistent skin ulcerations in adult rc mice suggest a defect in hair follicle (HF) keratinocyte stem cell (KSC) proliferation and epidermal maintenance. By contrast, the sebaceous glands in rc mice are hypertrophic due to sebocyte hyperplasia. Taken together, these abnormalities may be indicative of a switch in KSC fate. Previously, the rc locus was mapped close to the Mpi-1 gene on mouse chromosome 9, but the gene mutation remains to be identified. In our preliminary studies, we mapped the rc locus to a small interval containing 11 candidate genes. None of these genes has been shown to play a role in HF differentiation. The objective of this project is to identify the rc gene mutation and its effects on KSC properties in the re mice. We hypothesize that the normal re gene plays a role in KSC fate determination between the keratinocyte and sebocyte lineages, and that the mutation in the rc mice resulted in an increased commitment to sebaceous differentiation and a concomitant reduction in HF KSCs. To test our hypothesis, we will first identify the mutation in candidate genes within the minimal interval in the rc mice by sequence analysis. In the meantime, we will identify changes in HF KSC properties in the rc mice. We will test the hypothesis that there is a reduction in the number of HF KSCs and an increased proliferation of the sebocyte progenitors in the rc mice by BrdU labeling experiments. In addition, we will also identify the changes in the expression of critical genes involved in HF and sebaceous gland differentiation between the rc/rc and normal mouse skin. Finally, once the mutation is identified, we will identify changes in the rc RNA and protein expression in the rc mice. Our work will have a significant impact on skin and hair biology. We will identify a novel function of a previously known gene or a novel gene involved in keratinocyte stem cell fate determination and differentiation. Misregulation of KSC differentiation has been identified in a wide range of epithelial tumors. Results from this study may lead to a better understanding of the mechanisms of some of these tumors and new strategies for treatment.